Since 1959, there have been a number of explosions of the center wing tank on military and commercial aircraft reportedly resulting in deaths of as many as 550 persons. Those infrequent but continuing occurrences involving fuel tank explosions are believed to have possibly been caused by unknown sources of ignition, possibly initiated by conductive wires exposed to the explosive fuel vapor/air mixture in the tank. These accidents have added impetus to the search for an effective system for inerting flammable and potentially explosive vapors in fuel tanks, particularly of aircraft. Inerting systems using halogen-based gases have been known for use in military aircraft. But the use of halogen-based gases is not viable in commercial aircraft and in general aviation because of their effects resulting in ozone depletion. A non-halogen based system, moreover, would be advantageous in military applications as well because of the more environmentally friendly nature of an inerting system based on a non-halogenic gas.
A brief discussion of the history of the problem of center fuel tank explosions and of the growing interest in implementing an inerting system on commercial aircraft is found in Air Safety Week, Vol. 15 No. 16, Apr. 16, 2001, “Fatal Explosion Highlights Hazard of Flammable Vapors in Fuel Tanks.” The discussion in that article pointed out that, in particular, the center wing tank of commercial aircraft can reach high temperatures when the aircraft required to queue up on the hot tarmac of an airport at summer temperatures, and that such conditions have been linked to some explosions. The issue of Air Safety Week noted above also discusses a number of nitrogen based inerting systems that were considered by the Aviation Rulemaking Advisory Committee at its meeting of Apr. 4, 2001. Included among those systems was a brief discussion of the system of the present invention.